Although friendships are thought to play a key role in healthy adolescent development, this assertion has not been adequately investigated. Especially needed are longitudinal data that investigate the antecedents and consequences of individual differences in friendship. The proposed 3-year longitudinal study tracks young adolescents from sixth grade to eighth grade. The first aim is to evaluate the degree to which positive and negative features of friendship are linked to adolescent adjustment and to determine if these links grow stronger during early adolescence. Multi-method assessments will be made of individual adjustment and friendships during Year 1 and Year 3 of the study; assessments of relationships with mothers, fathers, siblings, and romantic partners will also be gathered at these times. These data will be used to evaluate changes in the impact friendship has on mental health (relative to that of other relationships) and will reveal whether changes in adolescent adjustment are causally linked to prior friendship experiences. The second aim is to determine if certain "mature" interpersonal competencies are needed to successfully forge close friendships during adolescence. During Year 1 and Year 3, multi-source questionnaire and observational assessments of interpersonal competence will be made and used to investigate the hypothesis that interpersonal competence is a causal antecedent of successful functioning in adolescent friendship. The third aim is to determine whether specific types of interactions with friends are responsible for subsequent changes in interpersonal competence and, in turn, whether interpersonal competence influences developmental changes in interactions with friends. A daily telephone interview technique will be used during Year 1, Year 2, and Year 3 to gather assessments of the frequency and quality of four types of interactions (disclosure, support, conflict, and rebuff). Structural equation modeling techniques will be used to evaluate whether changes in competence from Year 1 to Year 3 are accounted for by particular types of interactions in the intervening year. The fourth aim is to determine if adolescent's functioning in close friendships is forecast by prior family functioning or if discontinuities in development occur for a sizable number of children. Cluster analyses will be conducted to identify sub-groups that represent different "pathways" between family and peer relationships. These analyses will, for example, allow me to evaluate H. S. Sullivan's (1953) contention that positive experiences in close friendships during adolescence can help remedy adjustment problems stemming from a history of hostile or neglecting family relationships.